Method of cooling wafers

ABSTRACT

Methods and apparatuses are provided for cooling semiconductor substrates prior to handling. In one embodiment, a substrate and support structure combination is lifted after high temperature processing to a cold wall of a thermal processing chamber, which acts as a heat sink. Conductive heat transfer across a small gap from the substrate to the heat sink speeds wafer cooling prior to handling the wafer (e.g., with a robot). In another embodiment, a separate plate is kept cool within a pocket during processing, and is moved close to the substrate and support after processing. In yet another embodiment, a cooling station between a processing chamber and a storage cassette includes two movable cold plates, which are movable to positions closely spaced on either side of the wafer.

BACKGROUND OF THE INVENTION

This invention relates to methods and devices for cooling bodies such assemiconductor substrates after they are heated. More particularly, theinvention relates to cooling a substrate by heat transfer between thesubstrate and a heat sink prior to handling the substrate.

Semiconductor wafers or other such substrates are subjected to very hightreatment or processing temperatures. For example, in certain chemicalvapor deposition (CVD) processes, the temperatures can approach 1,200°C. In a typical cycle, a wafer is transferred from a room temperaturecassette by a robotic wafer handler into a processing or reactionchamber, where it is subjected to a high temperature treatment and isthen transferred by the wafer handler from the high temperatureprocessing chamber back to the same cassette or a separate cassette forprocessed wafers.

In many high temperature processes encountered in semiconductorprocessing, the wafer has to cool from the processing temperature to amuch lower temperature before it can be placed or picked up by a waferhandler. For example, in an epitaxial silicon deposition reactor,processing temperatures in the reaction chamber are typically in therange of 1,000-1,200° C., while the maximum temperature that the roboticwafer handler can handle is only about 900° C. Furthermore, at hightemperatures, the wafer is more vulnerable to physical damage which canbe caused by the wafer handler during transportation. Therefore, thewafer must be allowed to cool down from the processing temperature(e.g., to about 900° C.) before it can be handled and transferred bystandard handling equipment. Similarly, the wafer must be cooled down toeven lower temperatures for safe handling by other types of waferhandlers (e.g., paddles), and for storage in low cost cassettes.

The time required to cool down the wafer to handling temperatures can bevery costly to the integrated circuit manufacturer. Cool down ratesdepend in part upon the mass of the system being cooled, and have beenmeasured at about 45 seconds from 1,200° C. to 900° C. for a 200 mmwafer on typical susceptor. This cool down adds to the total cycle timefor each wafer and hence decreases the throughput of the system. Thiswill increase the cost of wafer processing.

Because of the high cost of semiconductor wafer processing equipment, itis critically important from a competitive standpoint to be able to keepthe expensive equipment in continued use, allowing increased throughput.At the same time, the wafer cooling technique employed must becompatible with the environment of the CVD processing apparatus andstringent purity requirements. Additionally, the cost of the techniquemust itself be low enough that there is a net reduction in the per-wafer cost of processing.

It is therefore an object of the present invention to provide a methodand apparatus to cool down a wafer quickly and in a uniform fashion froma high processing temperature to a temperature at which the wafer can bepicked up using a wafer handler and placed in wafer storage cassette.

SUMMARY OF THE INVENTION

In accordance with one aspect of the present invention, a method isprovided for treating substrates in a processing chamber. The methodincludes loading a substrate onto a support structure within thechamber. The substrate is heated to a treatment temperature and treatedat that temperature. After the substrate has been treated, an element ismoved within the chamber to bring the substrate and a cooling surface ofa heat sink into a cooling position. The substrate and cooling surfaceare maintained at the cooling position, in which the substrate losesheat to the cooling surface.

In accordance with another aspect of the present invention, a method isprovided for cooling a substrate after heating to a processingtemperature. The method includes moving the substrate from a firstposition to a second position in proximity to a cold element. Thesubstrate is maintained at the second position while heat transfers fromthe substrate to the cold element until it cools to a handlingtemperature which is lower than the processing temperature.

In accordance with another aspect of the present invention, a method isprovided for cooling a semiconductor substrate from a first temperatureto a second temperature. The method includes moving a cooling memberfrom a retracted position to a location adjacent and spaced from thesubstrate. In the retracted position, the cooling member has a thirdtemperature which is lower than the second temperature. The coolingmember is maintain in the adjacent position until the substrate cools tothe second temperature. The substrate is then lifted with substratehandling device.

In accordance with still another aspect of the present invention, aprocessing reactor is provided for treating substrates at hightemperatures. The reactor includes a heat source and a plurality ofwalls which define a process chamber. A substrate support structure ishoused within the chamber. The reactor further includes a heat sink anda movable element. A drive mechanism moves the movable element from afirst position to a second position. In the first position, a substrate(supported by the support structure within the chamber) can be treated.In the second position, the heat sink is spaced from the substrate by adistance sufficiently small to enable heat transport between the coldelement and the substrate.

In accordance with yet another aspect of the present invention, asubstrate processing system is provided with a high temperatureprocessing chamber, a substrate holder positioned within the chamber, acooling member, and a cooling shelter. The shelter is configured toshield the cooling member from heat during high temperature processing.A moveable arm, supporting the cooling member, is connected to a drivemechanism which can extend the moveable arm and cooling member from afirst position to a second position. In the first position, the coolingmember is proximate the cooling shelter, while in the second position,the cooling member is proximate the substrate holder.

In accordance with another aspect of the invention, a cooling mechanismis provided in a substrate processing system. The mechanism includes asupport structure configured to support a substrate, a first coolingelement and a second cooling element. These components are relativelymovable between a cooling position and a substrate load position. In thecooling position, the substrate is proximate and spaced between each ofthe first and second cooling elements. In the substrate load position, awafer handler can place the substrate upon the support structure.

Advantageously, the illustrated embodiments facilitate conductivelycooling a substrate, thus cooling the substrate significantly fasterthan by radiation alone. As the cooling methods and mechanisms do notrequire handling the substrate with a pick-up device, down time(specifically that caused by waiting for substrate to reach atemperature at which it can be safely handled) is significantly reduced.Additionally, the substrate can be cooled before moving it from thesupport structure within the process chamber, in accordance with certainof the above-noted aspects. Few moving parts are required to adapt theinvention to existing reactors designs. The faster cool down processwill allow a wafer or other substrate to be picked up from or placed ona susceptor in a shorter time, which enhances wafer throughput andultimately decreases cost of wafer processing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic cross-sectional view of a processing chamberconstructed in accordance with a first embodiment of the presentinvention, with the wafer in a processing position.

FIG. 1B illustrates the processing chamber of FIG. 1A, with the wafer ina cooling position.

FIG. 1C is a schematic cross-sectional view taken along lines 1C--1C ofFIG. 1A.

FIG. 2A is a schematic cross-sectional view of a processing chamberconstructed in accordance with another embodiment of the presentinvention, with the chamber in a processing mode.

FIG. 2B illustrates the processing chamber of FIG. 2A, with the chamberin a cooling mode.

FIG. 2C is a schematic cross-section taken along lines 2C--2C. of FIG.2A.

FIG. 3A is a graph plotting temperature against cooling time for aspacing of about 20 mm between a wafer surface and a cooling surface.

FIG. 3B is a graph plotting temperature against cooling time for aspacing of about 1 mm between a wafer surface and a cooling surface.

FIG. 4A is a schematic cross-sectional view of a cooling stationconstructed in accordance with a third embodiment of the presentinvention, with the station in a substrate load/unload position.

FIG. 4B illustrates the cooling station of FIG. 4A in a substratecooling position.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

While the invention is illustrated in the context of a single-wafer,horizontal gas flow reactor, it will be understood by one of ordinaryskill in the art that the cooling mechanism of the present invention isnot limited to any specific type of reactors or processing chambers.Rather, the skilled artisan will find application for the principlesdisclosed herein in connection with a number of different types ofprocessing chambers or reactors, including cluster tools, batchprocessing systems, vertical gas flow or showerhead systems, etc.Furthermore, while the applications have particular utility for coolingdown wafers before handling and removing the wafer from the processchamber, the principles disclosed herein have application whenever it isdesirable to cool a workpiece prior to handling or storage.

FIGS. 1A, 1B and 1C illustrate a processing chamber which incorporates acooling system constructed in accordance with a first preferredembodiment of the present invention. A portion of a processing chamber10 containing the cooling mechanism is shown. A wafer support structureincludes a susceptor 12 directly supporting a semiconductor wafer 14 orother processing substrate or workpiece (e.g., glass substrate). Thesusceptor 12, in turn, is supported by a spider 16 on at least threepoints. The illustrated susceptor 12 is disk-shaped, with a diameterlarger than that of the wafer 14, and the wafer 14 is placedconcentrically on the susceptor 16. An external drive mechanism or motor20 rotates a shaft 22, which extends through the bottom wall 19 of thechamber 10. The shaft 22, in turn, supports and drives the rotation ofthe spider 16, susceptor 12 and wafer 14.

The illustrated chamber 10 is defined by an upper wall 18 and a lowerwall 19, typically comprising quartz, which are substantiallytransparent to energy from radiant heat sources or lamps (not shown)outside the chamber 10. As the walls 18, 19 do not appreciably absorbthe radiant heat from the lamps while the susceptor/wafer combinationdoes absorb this heat, the chamber is conventionally referred to as a"cold wall" chamber. Forced fluid (e.g., forced air and/or circulatedliquid coolant) actively cool the walls 18, 19 by convection, aiding tokeep the walls 18,19 cooler than the susceptor 12 or wafer 14 housedwithin the chamber 10.

The shaft 22 can also be translated vertically. It will be understoodthat the vertical translation can be accomplished by the same motor 20which drives the rotation, or can be driven by a separate motor. It willbe further understood by one of skill in the art that whole shaft can beelevated, or a telescoping portion of the shaft can lift the spider 16,susceptor 12 and wafer 14. Alternatively, the shaft can extend throughthe spider and lift the susceptor directly. During lifting, the wafer 14remains directly supported by the same susceptor 12 (or other wafersupport structure) which supports the wafer during processing.

With reference to FIG. 1B, in operation, after the wafer 14 has beentreated at high temperature and needs to be cooled down prior tohandling, the wafer 14 is lifted until it is in a cooling positionproximate the upper wall 18 of the reactor or processing chamber 10.Preferably, the upper wall 18 has a flat inner surface substantiallyparallel with a wafer surface when the wafer 14 is in the coolingposition, forming a gap 24 as shown in FIG. 1b. As the upper wall 18 iscooler than the just-treated wafer 14, the wall 18 serves as a heatsink. In the illustrated embodiment, the wafer surface facing thecooling surface of the cold wall 18 is the same surface which wastreated during processing, due to the fact that the susceptor 12continues to support the wafer 14 while it is cooled.

The upper surface of the wafer 14 is brought close enough to the innersurface of the upper wall 18 that conductive heat transfer between thetwo contributes significantly to, and preferably dominates, the totalheat transfer. At high pressures, viscous flow is prevalent and the heatconductance of gases is independent of pressure. It is well known thatthe heat transfer rate of radiation depends upon the temperaturedifference between two objects, while the heat transfer rate ofconduction is determined by both the temperature difference and thedistance between the objects. In the illustrated embodiment, in additionto radiative heat transfer, heat is efficiently conducted through theambient gas (e.g., purge gas) across the gap 24.

It has been found that, under normal operating conditions of illustratedreaction chamber 10, conductive heat transfer contributes significantlyto the heat transfer when the gap 24 is less than about 5 mm. Preferablythe gap 24 is between about 0.2 mm and 3.0 mm, and more preferablybetween about 0.5 mm and 1.5 mm. For example, with a gap of 1 mm, thedominant heat transport mechanism is heat conduction through the gasphase. Thus the wafer/susceptor combination will cool down much fasterwhen proximate the cold wall than it does by radiation alone (e.g., whenthe gap 24 is larger than 20 mm). The cooling rates at a gap of 1 mm anda gap of 20 mm are given in FIGS. 3A and 3B, respectively, which arediscussed in more detail below.

Uniformity of the gap 24 and uniform temperatures across across the coldwall facilitate uniform heat transfer across the surfaces. Accordingly,the stresses of thermal non-uniformities and consequent warpage or otherdamage to the wafer 14 are avoided. Uniform heat transfer can be furtherenhanced by continuing to rotate the wafer 14 while cooling the wafer14, as shown in FIG. 1B.

After the wafer 14 cools sufficiently for pick-up device to safelyhandle it without damaging either the wafer or the pick-up device, thewafer 14 is lowered to a position at which it can be picked up. Apreferred pick-up device is illustrated in U.S. Pat. No. 4,846,102,which describes a pick-up wand which operates on the Bernoulliprinciple, shooting high velocity streams of gas at angles. When broughtclose to the top of a wafer surface, the gas streams create a lowpressure zone above the wafer, causing the wafer to lift. The disclosureof U.S. Pat. No. 4,846,102 is hereby incorporated by reference. Thiswand, which shall be referred to as a "Bernoulli wand" herein, cansafely pick up wafers at temperatures of about 900° C. or lower.

As noted, the same structure which directly supports the wafer 14 duringprocessing (namely, the susceptor 12) supports the wafer 14 as it ismoved into the cooling position. Accordingly, cooling of the wafer 14can be hastened without the need for a special high-temperature handlingdevice. Moreover, no additional transfer step is required, and risk ofdropping, scratching or otherwise damaging the wafer while it is stillhot is minimized.

The above-described embodiment also enables rapid cooling withoutincreasing the risk of particulate contamination of the chamber and thewafer. In the first place, since the cooling is conducted within theprocess chamber, movement is minimized. Secondly, while the upper wall18 is convectively cooled through forced air and/or circulated liquidcoolant, the wafer cooling is predominantly conductive. Accordingly, theincreased rate of wafer cooling is not accompanied by exposing the waferto increased forced air convection. Predominantly convective coolingmethods, in contrast, can achieve rapid cooling only at expense ofincreased particulate contamination of the wafer.

FIGS. 2A, 2B, and 2C. illustrate a processing chamber 28 constructed inaccordance with a second embodiment of the invention. For convenience,elements similar to those in FIG. 1 will be referred to by likereference numerals. As illustrated, the chamber 28 includes a coolingmember or plate 30, preferably stored within a pocket 32 outside theprocessing area, such that the plate 30 does not interfere with waferprocessing. In the illustrated embodiment, the pocket 32 is located atthe downstream end of the chamber 28, opposite the processing gas inletand wafer loading port. As shown in FIG. 2A, the plate 30 is mountedwithin the pocket 32, spaced from the surfaces of the pocket 32 bydistances or spacings 34, on a movable arm 36. The arm 36 extendsthrough the pocket 32 and is driven by a drive mechanism or actuator 38.

The illustrated plate 30 has a flat lower surface which is greater thanor equal to the surface area of the wafer 14, and preferably comprises amaterial with a specific heat capacity higher than that of wafer 14 orsusceptor 12. The thickness of movable plate 30 can be selected by theskilled artisan to balance the material costs and available space withadvantageously high total heat capacity. Desirably, the plate 30 has athermal mass greater than that of the wafer 14 to be processed. Thethermal mass of a solid, or its lumped thermal capacitance, is given bythe equation:

    C.sub.T =ρVc

where:

ρ=the density of the solid,

V=the volume of the solid, and

c=the specific heat (heat capacity) of the solid. Thus, for a givenmaterial and surface area, the thermal mass of the plate 30 is directlyrelated to its thickness.

As the pocket 32 is located outside the processing area, it is shelteredfrom and does not absorb the radiant heat directed at thewafer/susceptor combination, and thus remains relatively cooler than thewafer 14. Advantageously, surfaces defining the pocket 32 are activelycooled by convection, such as by a circulated coolant fluid (air orwater).

In operation, the plate 30 is kept in the pocket 32 while the wafer 14is subjected to high temperature treatment (e.g., epitaxial depositionat about 1,000° C. to 1,200° C.). The cooled pocket 32 keeps the plate30 cooler, preferably below the handling temperature (e.g., about 900°C. for the preferred Bernoulli wand). Desirably, the spacings 34 betweenthe surfaces of the plate 30 and the walls of the pocket 32 are lessthan about 5 mm, so that conductive heat transfer contributes to theheat exchange which keeps the plate 30 cool within the cooled pocket 32.Depending upon the ambient gas pressure and conductivity within thechamber 10, the spacing is preferably between about 0.2 m and 3 mm, andmore preferably between about 0.5 mm and 1.5 mm. Desirably, the wafer 14continues to rotate during the cooling process.

When the high temperature processing step is completed, the actuator 38drives the arm 36 to move the plate 30 over the wafer 14, such that theplate 30 is proximate the wafer 14. In the illustrated embodiment, plate30 is mounted parallel to the wafer 14 and in the appropriate verticalposition relative to the wafer (i.e., preferably vertically spaced byless than about 3 mm, more preferably between about 0.5 mm and 1.5 mm).Accordingly, the preferred actuator 38 moves the arm 36 and thus theplate 30 exclusively horizontally. It will be understood that, in otherarrangements, the plate 30 can be moved both horizontally and verticallyuntil it is in face-to-face relation, spaced from the wafer by adistance facilitating conductive heat transfer.

The vertical gap 24 between facing surfaces of the wafer 14 and theplate 30 is preferably as described with respect to the embodiment ofFIG. 1. Accordingly, the wafer/susceptor combination cools quickly byboth conductive and radiative heat transfer.

When the wafer 14 is cooled to the desired handling temperature (e.g.,about 900° C. for the preferred pick-up wand), the movable plate 30 ismoved back to the pocket 32. The heat absorbed from the wafer/susceptorduring the cooling is then absorbed by the actively cooled pocket 32, toreturn to its original idle temperature. In the interim, the waferhandler can pick up the wafer 14.

As with the first embodiment, the second embodiment facilitates coolingthe wafer 14 without requiring separate handling of the wafer 14.Accordingly, no special high temperature handler is necessitated.Furthermore, the mechanism of the second embodiment can be adapted tocool wafers within so-called "hot wall" chambers, as long as themoveable plate is maintained at a lower temperature than the handlingtemperature. While, in other arrangements, the plate itself can bedirectly cooled, the illustrated arrangement advantageously obviatesplumbing or other coolant communication through the movable arm.

In either of the above-described embodiments, the cooling rate ispreferably enhanced by introducing purge gas to the processing chamberduring the cooling step, as is known in the art. Any purge gasesconventionally used in this type of reactor and process can be used inthe present invention. Examples of suitable purge gases include argon,hydrogen, nitrogen, and helium. Most preferably, the purge gas is onewith a high heat conductivity, such as helium and hydrogen. Such purgegas can serve as a heat conduction medium between the substrate and thecooling element.

It will be recognized by the skilled artisan that other cooling methodscan also be employed within the processing chamber, in combination withthe illustrated mechanisms, thereby minimizing cool down times.

The cooling rate can be estimated by the following equation: ##EQU1##

The meanings of the symbols in the equation are given in the followingTable. Also given in the Table are the parameters defining initialcooling conditions. The cooling rates of the susceptor 12 and the wafer14 calculated from this equation using the parameters are plotted inFIGS. 3A and 3B, respectively. The only difference between these twocases is that the gap 24 (represented by d distance in the equation) is20 mm in the case shown in FIG. 3A, while the gap 24 is 1 mm in the caseshown in FIG. 3B.

                  TABLE                                                           ______________________________________                                        COOL DOWN RATE                                                                Constant                                                                      or                                                                            Variable                                                                             Definition     Units    Value                                          ______________________________________                                        C.sub.p                                                                              heat capacity per unit                                                                       J/m.sup.2 K                                                                            4620                                                  area for the                                                                  susceptor/wafer                                                               combination                                                            ε                                                                            susceptor emissivity    0.7                                            (T)    heat conductivity of gas                                                                     W/mK     -(0.5411 × 10.sup.-8) ×                                           T.sup.2                                                                       + (4.457 × 10.sup.-4) × T                                         + (6.866 × 10.sup.2)                                                    (for H.sub.2)                                  T.sub.s                                                                              starting temperature                                                                         K        1473                                           T.sub.w                                                                              wall temperature                                                                             K        773                                            d      gap size       m        20 × 10.sup.-3  (FIG. 3A)                                               1 × 10.sup.-3  (FIG. 3B)                 ε.sub.w                                                                      wall emissivity         0.7                                            σ                                                                              Stefan Boltzmann                                                                             W/m.sup.2 K.sup.4                                                                      5.6 × 10.sup.-8                                 Constant                                                               ______________________________________                                    

Preferably, the cooling step takes less than about 60 seconds, and morepreferably less than 10 seconds to cool a wafer/susceptor combinationfrom 1,000° C.-1,200° C. to less than or equal to about 900° C. It canbe seen from FIGS. 3A and 3B that it takes about 17 seconds to cool thewafer 14 from 1,200° C. to 900° C. when the gap 24 is 20 mm (see FIG.3A), while it takes only about 4 seconds when the gap 24 is 1 mm (seeFIG. 3B). This calculation shows a significant difference in coolingrate caused by reducing the distance between the cold wall and the wafersurface. When it is cooled to a lower temperature, the differencebecomes even bigger, as heat transfer by radiation is less dominant atthese lower temperatures.

The above-noted calculations are given for a wafer and susceptorcombination, and particularly for a silicon carbide susceptor with athickness of about 0.7 mm and 200 mm wafer with a similar thickness. Itwill be understood, however, that similar calculations can be performedfor cooling the wafer alone, or for cooling the susceptor alone. Forexample, if it is desired to cool a susceptor after a process in whichno wafer is involved (e.g., chamber/susceptor etch process for cleaningbetween wafer processing steps), the susceptor alone can be brought inproximity to the chamber cold wall, or a heat sink can be brought inproximity to the susceptor.

The shorter the cooling period in the processing chamber 10, the soonerthe wafer can be removed and another wafer fed into the processingchamber 10 for continued production. Thus, in one implementation, thewafer 14 is removed from the processing chamber 10 when it is cooledfrom a processing temperature of 1,000° C.-1,200° C. down to about 900°C. In another implementation, the wafer 14 is removed from the processchamber with a more sensitive wafer handler after processing at greaterthan 600° C. down to a handling temperature below 600° C. The wafer canthen be further cooled down to a temperature at which it can be storedin a cassette. For example, the wafer can be maintained on a waferhandling device or at some off-line location until it cools to about100° C. See the description below of FIGS. 4A and 4B.

As will be readily apparent to the skilled artisan, the coolingmechanisms and methods disclosed herein can be adapted to any suitableconventional processing chambers. For example, the rotatable substratesupporting mechanism disclosed in U.S. Pat. No. 4,821,674, which isincorporated herein by reference, can be used in the present inventionfor supporting and controlling the movement of the wafer/susceptor.Similarly, the cooling mechanism of the present invention can be readilyadapted to a reaction chamber of the type disclosed in U.S. Pat. No.5,020,475, the disclosure of which is also incorporated herein byreference. The skilled artisan will recognize that a variety of methodsfor cooling a wafer substrate outside the processing chamber can be usedin combination with the above-described precooling processes andapparatuses for use inside the processing chamber.

Moreover, as demonstrated by the embodiment of FIGS. 4A and 4B, themethods and structures disclosed above can be adapted to non-processingchambers. FIG. 4A illustrates a cooling station 50 in a separate chamberoutside of a processing chamber. For example, the illustrated structurecould be employed in a wafer handling chamber between wafertransfer/storage cassettes and the processing chamber, or in a separatecooling chamber in a cluster tool. While cassettes are available thatcan handle wafers as hot as 170° C., they are relatively expensive. Acommonly available less expensive one made of Delrin® can only handletemperatures well below 100° C. Other commonly available units can onlyhandle about 60° C.

The illustrated cooling station is configured for use in conjunctionwith a handler which provides both a Bernoulli wand and a paddle. Acomplete description of such an arrangement is disclosed in U.S. patentapplication Ser. No. 08/784711 filed Jan. 16, 1997, which isincorporated herein by reference.

FIG. 4A shows the wafer 14 supported between an upper chamber wall 52and lower chamber wall 54, where the station 50 is an a waferload/unload mode. A wafer support structure defines a position at whichthe substrate is supported. In the illustrated embodiment, the wafersupport structure comprises a plurality of support pins 56 (at leastthree) positioned to stably support the wafer 14 horizontally.

When first loaded onto the pins 56, the wafer 14 can be at anytemperature higher than the desired handling or storage temperature. Inan exemplary implementation, the wafer 14 is transported from a thermalprocessing chamber upon a high temperature handler. The initial wafertemperature thus ranges from about 200° C. to 1,500° C., depending uponthe process to which it was previously subjected and the temperaturetolerance of the high temperature wafer handler. In the illustratedembodiment, the initial wafer temperature is between about 600° C. and1,200° C., and particularly about 900° C., transported by a wandoperating on the Bernoulli principle.

Between the supported wafer 14 and the upper wall 52, a first or uppercooling member 58 is supported above the wafer 14. The upper coolingmember 58 is shown movably supported by a piston 60 which extendsupwardly through the upper chamber wall 52, where the piston 60 connectsto a first or upper actuator 62. The cooling member 58 is preferablyactively cooled between cooling steps, and more preferably iscontinually cooled while wafers are being processed through the system.For example, the piston 60 can include internal plumbing to circulatecoolant which convectively cools the cooling member 58 in both thepositions of FIG. 4A and the position of FIG. 4B, discussed below.

In the illustrated wafer load/unload position, the upper cooling member58 is spaced sufficiently above the wafer to provide clearance for thepreferred high temperature wafer handler to load or drop off the wafer14 at the cooling station 50. It is advantageous to be able to use thehigh temperature wand because it does not touch the upper surface of thewafer and cools the wafer 14 convectively as the wafer 14 istransported.

In other arrangements, the upper cooling member can be moved to providesuch clearance only in a wafer loading mode, while it can be keptproximate to the wafer in both substrate cooling (FIG. 4B) and waferunloading modes. In still other arrangements, where both loading andunloading are performed by a wafer handler which supports the wafersolely from beneath the wafer (e.g., paddle or fork), such clearanceneed not be provided, and the upper cooling member can be fixed at aposition proximate the upper wafer surface.

The cooling station 50 also includes a second or lower cooling member64, supported between the wafer 14 and the lower chamber wall 54. In theillustrated embodiment, the lower cooling member 64 is movably supportedby a post 66, shown extending through the lower wall 54 to a second orlower actuator 68. The lower cooling member 64 is desirably alsoactively cooled.

As with the upper member 58, the lower cooling member 64 is spaced belowthe wafer 14 to allow access by a wafer handler, particularly a paddlewhich is well adapted for moving a wafer into and out of a commoncassette for wafers. Further, using the paddle for transporting a waferbetween the cassette and the cooling station is desirable because itfits between wafers in a standard cassette. For example, a lowtemperature wafer handler for unloading the wafer from the station 50can comprise a fork or paddle which extends beneath the wafer 14 amongthe pins 56. Once beneath the wafer 14, the handler lifts the wafer 14only slightly to clear the pins 56, and transports the wafer 14 to awafer storage cassette in a load lock chamber.

In other arrangements, the lower cooling member can be lowered toprovide such clearance only in a wafer unloading mode, while it can bekept proximate to the wafer in both substrate cooling (FIG. 4B) andwafer loading modes. In still other arrangements, where both loading andunloading are performed by a wafer handler which supports the wafersolely from above the wafer (e.g, a handler operating on the Bernoulliprinciple), such clearance need not be provided, and the lower coolingmember can be fixed at a position proximate the lower wafer surface.

With reference now to FIG. 4B, the cooling station 50 is illustrated ina substrate cooling position. As shown, the upper cooling member 58 islowered to a position in proximity to the upper surface of the wafer 14,such as to allow heat transfer from the wafer to the cooling member 58.The gap between parallel surfaces of the upper cooling member 58 and thewafer 14 is thus less than about 5 mm, preferably between about 0.2 mmand 3 mm, and more preferably between about 0.5 mm and 1.5 mm.

Preferably, the lower cooling member 64 is also raised to a positionproximate the lower surface of the wafer 14, such as to allow heattransfer from the wafer to the lower cooling member 64. The gap betweenthe lower cooling member 64 and the wafer 14 is thus as described withrespect to the upper cooling member 58.

Desirably, the cooling station 50 provides for conductive heat transferfrom two opposite side of the wafer 14, thus rapidly cooling the wafer.As the cooling station 50 operates to cool the wafer 14 to lowertemperatures than the previously described embodiments, this doubleconductive heat transfer is particularly advantageous, as radiative heattransfer is less dominant at lower temperatures. Desirably, the coolingstation 50 is is maintained in the cooling position until the wafer 14cools to a temperature which the handler and/or cassette can tolerate.Thus, the station 50 is preferably kept in the cooling position untilthe wafer 14 cools to less than about 170° C. prior to unloading thewafer 14 for storage in a high temperature cassette. In otherarrangements, the wafer 14 is preferably cooled to less than about 100°C. or 60° C., depending upon the temperature sensitivity of the cassettebeing employed.

It will thus be appreciated that the substrate cooling systems describedabove have great flexibility and can be adapted to many differentexisting systems. The embodiments disclosed herein facilitate rapidcooling prior to handling the wafer. The wafer can thus be more quicklyremoved from the processing chamber so that the chamber is sooner freeto process a second substrate. Similarly, substrate can be cooled to acassette storage temperature more rapidly, such that cooling for storageis does not limit the rate at which substrates are passed through aprocessing system. The cooling of the wafer is greatly promoted bybringing the wafer surface proximate a heat sink, or vice versa, priorto handling the wafer. The heat sink can be a cold element of thereactor, or a separate cold element installed in the processing chamberfor this purpose. The particular heat sink can be made any suitableshape in various embodiments. Advantageously, however, the coolingsurface of the reactor wall or the plate is planar and substantiallyparallel to the treated surface of the wafer, and thus is face-to-facerelation, when the system is in a cooling mode. In this manner, thewafer need not be removed from the wafer support structure for theprecooling step.

The distance between the cooling surface and the wafer surface can bemade as small as possible. Preferably, however, the wafer and coolingsurfaces do not touch each other. For normal operation, the gap ispreferably less than about 3 mm, more preferably between about 0.5 mmand 1.5 mm, and most preferably about 1.0 mm. The cooling can beconducted at any pressure, for example, at atmospheric pressure or underreduced pressure, as long as the pressure is in the viscous regime.

It will be appreciated by those skilled in the art that variousmodifications and changes may be made without departing from the scopeof the invention. Such modifications and changes are intended to fallwithin the scope of the invention, as defined by the appended claims.

What is claimed is:
 1. A method of treating substrates in a processingchamber, comprising:loading a substrate onto a support structure withinthe processing chamber; heating the substrate to at least one treatmenttemperature; treating the substrate at the treatment temperature in atreatment position within the processing chamber; after treating thesubstrate, moving an element to bring the substrate and a coolingsurface of a heat sink into a cooling position within the processingchamber wherein the substrate loses heat to the cooling surface; andmaintaining the substrate and the cooling surface in the coolingposition.
 2. The method of claim 1, wherein the substrate and thecooling surface are spaced by between about 0.2 mm and 3.0 mm in thecooling position.
 3. The method of claim 1, wherein the substrate andthe cooling surface are spaced by between about 0.5 and 1.5 mm in thecooling position.
 4. The method of claim 1, further comprising removingthe substrate from the support structure after maintaining the substrateand the cooling surface in the cooling position, removing the substratefrom the chamber, and loading a second substrate onto the supportstructure.
 5. The method of claim 1, wherein moving the elementcomprises moving the heat sink.
 6. The method of claim 1, wherein theheat sink is actively cooled.
 7. The method of claim 6, furthercomprising withdrawing the heat sink from the cooling position to anactively cooled location after maintaining the substrate and the coolingsurface in the cooling position.
 8. The method of claim 6, wherein theelement comprises the support structure, and further comprisingwithdrawing the element from the cooling position prior to removing thesubstrate from the support structure.
 9. The method of claim 1, whereinthe heat sink comprises at least a portion of a wall of the processingchamber, and moving the element comprises moving the support structure.10. The method of claim 1, wherein the heat sink comprises a coolingplate, and moving the element comprises moving the plate.
 11. The methodof claim 1, wherein the cooling surface is substantially parallel to asurface of the substrate in the cooling position.
 12. The method ofclaim 1, further comprising providing a purge gas to the chamber whilecooling the substrate.
 13. The method of claim 1, wherein a chamberpressure is maintained at a level resulting in viscous flow between thesubstrate and the cooling surface in the cooling position.
 14. Themethod of claim 1, wherein the substrate remains supported upon thesubstrate support structure in each of the treatment and coolingpositions.
 15. The method of claim 1, further comprising rotating thesubstrate in the cooling position.
 16. The method of claim 1, whereinthe support structure comprises a susceptor.
 17. A method for cooling asubstrate after treating the substrate at at least one processingtemperature while supported at a first position in a processing chamber,the method comprising moving the substrate from the first position to asecond position within the processing chamber proximate a cold element,maintaining the substrate at the second position, and transferring heatfrom the substrate to the cold element until the substrate reaches ahandling temperature lower than the processing temperature.
 18. Themethod of claim 17, wherein the cold element comprises a cold wall ofthe processing chamber, the wall comprising a material substantiallytransparent to radiant heat.
 19. The method of claim 18, wherein thewall is actively cooled by forced convection.
 20. The method of claim18, wherein the substrate has a surface, the cold wall has a flat innersurface, and the surfaces are positioned facing and substantiallyparallel to each other in the second position.
 21. The method of claim20, wherein the upper surface of the substrate and the inner surface ofthe cold wall are substantially horizontal in each of the first andsecond positions.
 22. The method of claim 17, wherein adjacent surfacesof the substrate and the cold element are spaced apart by between about0.2 mm and 3 mm in the second position.
 23. The method of claim 17,wherein adjacent surfaces of the substrate and the cold element arespaced apart by between about 0.5 mm and 1.5 mm in the second position.24. The method of claim 17, wherein the processing temperature isbetween about 1,000° C. and 1,200° C., the handling temperature is lessthan about 900° C., and the substrate is maintained at the secondposition for less than about 60 seconds.
 25. The method of claim 24,wherein the substrate is maintained at the second position for less thanabout 10 seconds.
 26. The method of claim 17, wherein the processingtemperature is between about 600° C. and 1,200° C., the handlingtemperature is less than about 600° C., and the substrated is maintainedat the second position for less than about 60 seconds.
 27. The method ofclaim 26, wherein the substrate is maintained at the second position forless than about 10 seconds.
 28. The method of claim 17, wherein thesubstrate is supported by a substrate support structure in each of thefirst and second positions, and moving the substrate comprises movingthe substrate support structure.
 29. The method of claim 17, wherein thesubstrate support structure comprises a susceptor supported by a shaft,and moving the substrate support structure comprises verticallyextending the shaft upward toward the cold element.
 30. A method ofcooling a semiconductor substrate from a first temperature to a secondtemperature within a processing chamber, the method comprising:moving acooling member from a retracted position to a location adjacent andspaced from the substrate, the cooling member having a third temperaturein the retracted position, the third temperature lower than the secondtemperature; and maintaining the cooling member adjacent and spaced fromthe substrate until the substrate cools to the second temperature; andlifting the substrate with a substrate handling device after thesubstrate cools to the second temperature.
 31. The method of claim 30,wherein the cooling member is within an actively cooled structure at theretracted position.
 32. The method of claim 30, further comprisingwithdrawing the cooling member from the location adjacent the substrateto the retracted position after the substrate cools to the secondtemperature.
 33. The method of claim 30, wherein moving the coolingmember comprises horizontally translating the cooling member to thelocation adjacent the substrate, the cooling member having a coolingsurface substantially parallel and vertically spaced from an uppersurface of the substrate.
 34. The method of claim 33, wherein the uppersurface of the substrate is spaced by between about 0.5 mm and 1.5 mmfrom the cooling surface of the cooling member.
 35. The method of claim33, wherein the cooling member is sheltered within the processingchamber from a heat source at the retracted position.
 36. A method ofcooling a semiconductor substrate from a first temperature to a secondtemperature within a chamber, the method comprising:moving a coolingmember from a retracted position to a location adjacent and spaced fromthe substrate, the cooling member having a third temperature in theretracted position, the third temperature lower than the secondtemperature; and maintaining the cooling member adjacent and spaced fromthe substrate until the substrate cools to the second temperature;lifting the substrate with a substrate handling device after thesubstrate cools to the second temperature; and moving a second coolingmember to a position adjacent and spaced from the substrate on anopposite side of the substrate from the cooling member, andsimultaneously transferring heat from the substrate to each of thecooling member and the second cooling member.
 37. The method of claim36, wherein the second cooling member comprises a movable platformbeneath a wafer supported on pins.
 38. The method of claim 36, whereinthe chamber comprises a cooling chamber adjacent a substrate processingchamber.